text: Cytochrome c oxidase has 3 subunits which are encoded by mitochondrial DNA (cytochrome c oxidase subunit I, subunit II, and subunit III). Of these 3 subunits encoded by mitochondrial DNA, two have been identified in extramitochondrial locations. In pancreatic acinar tissue, these subunits were found in zymogen granules. Additionally, in the anterior pituitary, relatively high amounts of these subunits were found in growth hormone secretory granules. The extramitochondrial function of these cytochrome c oxidase subunits has not yet been characterized. Besides cytochrome c oxidase subunits, extramitochondrial localization has also been observed for large numbers of other mitochondrial proteins. This raises the possibility about existence of yet unidentified specific mechanisms for protein translocation from mitochondria to other cellular destinations.